Summary The flight crew of the Boeing 727-200 were completing a regularly scheduled passenger flight into Calgary, Alberta. Because of poor weather in Calgary, the flight was delayed for one and a half hours in Salt Lake City, Utah, extending the crew's scheduled duty day. In Calgary, the crew conducted a flap-30, autopilot-coupled, instrument landing system approach in low visibility to runway 34. The autopilot was disconnected at about 130 feet above ground level. During the landing, the right wing struck the runway. There was damage to the wing tip, the leading edge flaps, the trailing edge flaps, the flap screw-jack, and track fairings of the right wing. The crew was not aware that the wing had struck the runway until the post-flight inspection was completed on the Calgary ramp. No one was injured in the accident. Ce rapport est galement disponible en franais. Other Factual Information The flight crew's operating base was Atlanta, Georgia. The captain and the second officer lived outside of the Atlanta area and commuted by air to their base. On the day of the occurrence, the captain arrived at the Charleston, South Carolina, airport for his commute flight at about 0700 eastern standard time (EST).(1) After arriving in Atlanta, the captain spent his time in the company operations office until his crew check-in time of 1225. During that time, he reviewed flight information and his company mail. The second officer arrived at the Nashville, Tennessee, airport at about 0830 for his commute flight and also spent his time in the company operations office. The first officer arrived shortly before the crew check-in time, after a one-hour drive from his home in Macon, Georgia. The crew were scheduled for an 11 hour 30 minute duty day, with the duty day ending in Calgary, Alberta. The crew operated the flight from Atlanta to Minneapolis, Minnesota, and then on to Salt Lake City, Utah. There was a 2 hour 30 minute scheduled wait in Salt Lake City before they were to operate the flight to Calgary. The flight arrived at Salt Lake City close to the scheduled time, and the crew waited in the terminal building for their next flight. The captain and the first officer spent some of this ground time reviewing various company documents, including safety information that highlighted the problem of Boeing 727 wing strikes during landing. After the passengers for the flight to Calgary had been boarded, the crew received information from their dispatch that the Calgary weather had gone below their landing limits. The decision was made to keep the passengers on board and then depart when the weather improved. After receiving a report of improved weather, the flight departed for Calgary about 1 hour 30minutes late. The actual duty day until the crew disembarked at Calgary was about 13 hours 15 minutes. The Delta pilots' association agreement with the company allows a maximum scheduled duty day of 13 hours. The company flight operations manual and the pilots' association agreement with the company permit flight crews to exceed the scheduled duty day by two hours for irregular operations such as weather problems. The company indicated that a large percentage of its crews commute by air to their operating base. One estimate provided by the company indicated that 38 per cent of the Atlanta-based pilots commute by air; a large number of cabin crew members also commute by air. Crew members who commute by air typically do not take the last possible flight to their operating base because they require a back-up plan in case their commute flight is delayed or cancelled. The company expects that crews will leave themselves options so they arrive in time for their duty flight. There are no instructions to the company's crews regarding the requirement to pre-position themselves at their operating base the night before a scheduled duty day. The occurrence crew were operating under the flight time limitations and rest requirements of the United States Federal Aviation Regulations (FARs). The FARs are silent on the subject of crews who commute by air to their operating bases. Canadian Aviation Regulations do not specifically address the subject of commuting by air either. Runway 34 at the Calgary airport is 12 675 feet long and 200 feet wide. The runway threshold elevation is 3 543 feet above sea level (asl). The decision height for the Category 1 instrument landing system (ILS) approach is 3 743 feet asl, which is 200feet above ground level (agl). Runway 34 is equipped with medium-intensity runway-edge lighting and high-intensity approach lighting with runway alignment indicator lights. There is no centreline lighting on runway 34. The ILS has a three-degree glide slope and was serviceable at the time of the occurrence. As with most airports in Canada,(2) the runway is not equipped with a middle marker. At the time of the occurrence flight's approach, the reported weather was as follows: obscured ceiling at 100 feet agl, visibility 0.5 statute mile in freezing fog, temperature minus four degrees Celsius, dewpoint minus five degrees Celsius, altimeter setting 30.00 inches of mercury, and wind 140 degrees true at four knots. The tower controller reported the runway visual range as 5000 feet, with a runway light setting of five. The crew of another aircraft, which landed about two minutes before the occurrence aircraft, indicated that there was a slight wind from the east but very little drift. They observed the runway environment at about 100 feet above the decision height. At first only the approach lights could be seen, then they could see the 1 000-foot lighting bar, followed by the end of the runway. During the landing by the occurrence aircraft, the crew noted that the visibility was very limited until just before touchdown. The aircraft weight at the time of the approach into Calgary was about 154 000 pounds, 500 pounds below the maximum landing weight. This is a heavier-than-normal landing weight because of the additional fuel carried on board in the event poor weather in Calgary forced the aircraft to return to Salt Lake City. The landing reference speed (Vref) for a flap setting of 30degrees at the occurrence weight is 134 knots indicated airspeed (KIAS); a flap 40-degree Vref is a couple of knots lower. A straight-in autopilot-coupled approach was conducted to runway 34; the crew planned to use the autopilot to just above its minimum operating altitude of 50 feet agl. The aircraft intercepted the ILS glide path at 6 000 feet asl and made a continuous descent on the glide path. Based on the flight data recorder and the radio transmissions, it was estimated that the aircraft descended through 1 500 feet radio-altimeter height at about 0121:12. The approach was flown at 142 KIAS, which yielded a true airspeed of 146 knots. The recorded radar data revealed that the average ground speed during the descent was 155 knots. The aircraft was stabilized on the glide path until about 350 feet agl. At this point (about 84 seconds after descending though 1500 feet agl), the aircraft pitched from 2 degrees nose-up to about 4 degrees nose-up. The aircraft then pitched down to 1degree nose-up, then began pitching up again about 98 seconds after descending below 1 500 feet radio-altimeter height. A pitch angle of 5 degrees nose-up was reached just as the aircraft was descending through the decision height. The aircraft then pitched down again and reached a pitch angle of slightly less than 0 degrees. The captain disconnected the autopilot when the nose-down pitch was sensed during this pitch-down. The aircraft passed through 50 feet agl about 110 seconds after descending below 1 500 feet radio-altimeter height. Just after the autopilot was disconnected, the aircraft started to drift left of the runway centreline. The captain attempted to correct back to the right by using right bank. The aircraft touched down during this banked turn. The bank angle during the initial touchdown was about 9 degrees, and the recorded vertical acceleration was 1.35 times the force of gravity (g). A second touchdown followed, with a recorded vertical acceleration of 1.54 g and an increased bank angle of about 12 degrees. The recorded time of the landing was 0123:07. The Boeing 727 Operations Manual, Normal Procedures, states: The B727-200 aircraft have experienced numerous incidents involving tail-skid or wing-tip contact with the runway. . . . . As a result of pronounced sweep-back, a small increase in pitch dramatically increases the risk of wing-tip contact with the runway. It is possible to make contact with as little as 7 of roll where a firm landing is made with a corresponding degree of pitch-up. The aircraft was equipped with a Sperry SP-150 autopilot. As with most autopilots, the autopilot sensitivity is designed to decrease as the aircraft gets closer to the ground during a coupled approach. The purpose of this sensitivity reduction is to eliminate overcontrolling by the autopilot. Small physical displacements from the glide path or localizer create large apparent angular displacements that the autopilot would otherwise attempt to correct too violently. The Sperry SP-150 autopilot is designed to desensitize over a 150-second period after the radio altimeter senses a height of 1500 feet agl. During the 150 seconds, the sensitivity (or gain) reduces to 22 per cent of the normal value. If a middle marker is sensed on the approach, before reaching the 150-second point, the gain would reduce to 22 per cent at twice the previous rate. The gain would then decrease to about 6 per cent of normal within another 30 seconds. During descent, this time-based design will properly schedule the desensitization only if the distance from the runway is consistent with a 3-degree glide slope and if the aircraft's actual ground speed is relatively close to the assumed ground speed designed into the autopilot. If the ground speed is higher than the design-assumed ground speed, the airplane will approach the runway before the desensitization period expires, and the sensitivity will be higher than that intended by the design. One assumption in the designed ground speed was that approaches would be flown using a flap setting of 40 degrees; however, a 30-degree flap setting is now the standard practice. The lower flap setting results in a higher approach speed. Recognizing that the normal approach flap setting is now 30 degrees, Sperry issued a service bulletin (SB) for the SP-150 autopilot. By complying with SB 21-1132-122, the SP-150 autopilot time to desensitize was reduced to 105 seconds. Compliance with the SB is not mandatory, and the occurrence Boeing 727 autopilot did not have the SB modification. The Boeing 727 is not certified for a Category II landing with an SP-150 autopilot when the middle marker is not available, unless a modification has been made to provide approach gain change via the Low Range Radio Altimeter system. The occurrence aircraft did not have this modification. The United States National Transportation Safety Board (NTSB), while investigating a 1998 accident at Chicago O'Hare International Airport, Illinois, determined that in some instances 150 seconds is too long to provide the desired autopilot sensitivity reduction. Pitch oscillations close to the ground can then occur. On 01 June 2000, the NTSB issued five recommendations (A-00-41 through A-00-45) to deal with the problem of the Sperry SP-150 (and SP-50) autopilot sensitivity. The NTSB recommendations are contained in AppendixA.